Field of the Invention
The present invention relates to an objective optical system for endoscope, and particularly to an objective optical system for endoscope which can be used in an endoscope apparatus that is used in a medical field or an industrial field.
Description of the Related Art
An endoscope is an apparatus that has been used widely in the medical field and the industrial field. In the medical field in particular, images achieved by an endoscope inserted into an abdominal cavity have been used for diagnosis and treatment of a site observed.
In an optical system of an endoscope, by setting an appropriate F-number, it is possible to achieve a focused image from a near-point object up to a far-point object. Moreover, by making small a lens diameter and an overall optical length, is possible to arrange an endoscope having a small diameter, which does not cause pain while being inserted, and which is capable of turning in a small radius inside the body. In recent years, endoscopes with even superior image quality and further smaller size have been sought.
As an objective optical system for endoscope of a small size, there are objective optical systems proposed in Japanese Patent Application Laid-open Publication No. 2004-061763, Japanese Patent Application Laid-open Publication No. 2009-223183 and International Unexamined Patent Application Publication No. 10/119640.